Fusion photothermography



April 11, 1950 MURRAY 2,503,758

FUSION PHOTOTHERMQGRAPHY Filed Au 16, 1947 v 5 Sheets-Sheet 1 ALEXANDER MURRAY INVENTOR BYE j 120 I ATTORNEYS Ap 11, 1950 A. MURRAY FUSION PHOTOTHERMOGRAPHY I 3 Sheets-Sheet 2 Filed Aug. 16, 1947 FIG.5.

Q FIGMS.

ALEXANDER MURRAY I/NVENTOR BY g ATTORNEYJ SIDE [BEE GEES BEBE 14a I47 146 14s April 11, 1950 A. MURRAY 2,503,758

- FUSION PHOTOTHERMOGRAPHY 3 Sheets-Sheet 3 Filed Aug. 16, 1947 ALEXANDER MURRAY INVENTOR W WW 395v ATTORNEYS Patented p 11, 1950 v r TiED PATENT OFFICE -FUSIONPHI)'ITDTHERMO'GRAPHY Alexander :Murray, iRochester, .-;N. assignor .;.to Eastman .Kodak Company, Rochester, .N. Y.,. a icorp'orationlofwNewiJersey *Applicati'on Augustlfi, 1947,SerialNo. 768,977

13:..Claims. 7.1 "Thisainvention'rlates to 'fusion photothermography and. is 'particularly"directed to -'-a preferred species *thereo'f. "Fusion photothermography is described generically in "my application, Serial Number 768j979,fi1ed concurrently herewith.

The object oithe present'invention is to -provide asimplefihigh' quality printing process-which re quires onlyinexpensiveequipment. 1 One particular advantage of the present embodiment is the fact that 'it is 'direotly adaptable "to multi-color printing. Tour-color prints, for example, produced-bythe-present invention have been found to" have quite-satisfactoryquality.

pointed out in the above mentioned-concurrently 'file'd-:application, fusi'onphotothermographyrequire's a uniform la'.-yer"o'f coloring material-in a fusiblewhiole'maintained ata uniform temperature just below the melting point'of'the vehicle. A negative "two tone "heat -im age applied totl'iis'layer*differentially *fuses 'the ink vehicle to --'a support such as paper. 'The distinguishing feature of the present invention is the'manner inwhich-this negative heat image isobtained. A twotone image is formed as A a positive in heat absorbing material. 'For example, "a positive transparency made "on extremely high contrast film having only "a 'very' thin -emulsion, is coated with'a powdered 'fusible inkan'd then uniformly irradiated with'infrared light. flh'e radi-ation is absor'be'd"-by the "silver 'grains in the 'dark areas of the 1 positive whioh heats these areas and= melts the "ink adjacent thereto while the ink adjacent to'clear areas of the-filmremainsunmelted. Note that the dark "areas or the positive "are the hot ones so that the heat image is a negative one. 3

Themlte'd areasof ink are immediatelytransferred to amapensupport bypressing it into "contact withthe positive record. The unmelted par-ts dfithe'ink are then removedby'brus'hing, mechanically or with air, from both the paper and the =positivezlfi1m record which is i immediately reinke'dandiused; over again.

' It common parlance :to refer :to materials which .1 absorb radiation and cgetrhotrasheatsabsorbers, Irbut in :the accompanying claims the critically precise. phrase fmaterialxwhich' absorbs radiation rand roonverts it 2 to heat is used since the actual operation is the conversionioi-radiant energyiintoiheatz.energy.

.Asmoments :reasoning ;shows"that T the :positive record in sheat absorbing imaterialf; must "be ."on 1a support of low heatiabsorpti'on,.tbutreven zaathin .layer'ofifilma'orzglass hasiaprovensadequate forithis .pu1:.puse :andithewholerrecordtmay beilying am ;a

.2 lhesexposure'to infraretlilig'ht may be either fro theffrontthrough the ink layer=or from-the rear through the transparent film ibase. "Experience has =shown that more-satisfactory results are obtained when the exposure is from the Tfront through the ink layer rather than through the film. Various possibleexplanations of this difference-have been proposed but none of them has specifically *led to any "further -"discoveries and therefore thereissno'point in considering them.

The ink may be-roll'ed onto the record; or dusted ento' -the record, or pre='formed= into a thin sheet which is :applied to the *record by passing both between :pressure rollers. The vehicle-of -'the layer :should have a melting point "above room temperature for 'convcnien'ce in operation "of the invention and the temperature should-not be too high since it "would *become difiicult'tocontrol temperatures greater than ZOG E. Pre'ferably the melting point should be between 30 C. 'and C. for most convenient operation. For most rapid printing, -'the ink 'sh'ould be preheated to Within one or two-'d'egrees-oi its melting *point, at -lea-s't within 20 thereo The pap'eraorother support-whichis to receive the final' print image-by fusion with the 'melted areas "of the "ink shotilcl pri zfer-ably be at a temperature 'below the melting 'pointof the ink so that -the ink solidifies immediately after fusion to =the paper. The invention and-preferred embodiments -thereof-will =be=f1illy understood from the following description *when read in -:connection :withthe accompanying drawings, in which:

Fig. 1 illustrates schematicallyin-'cross section a preferred em'bodiment-of the invention.

Fig. 2 similarly illustr-ates "an alternative arrangement of one of the features of Fig. '1.

Fig. -3is=a greatly magnified cross-section of a printing plate :during I the exposing :operation of the invention.

iFigaii schematically illustrates anembodimen't :of the .iinvention alternative :to that shown in FigJl.

.iE'ig. :5 similarly :illustrates a hig'hly automatic :and f continuous :embodiment :of the invention.

.Fig. 16; is'sa top view of aa zsimple*iourwolonpress employing :the invention.

Fig. 7 is a front view of a four-color press 'employing an embodiment 'of tthe I invention.

Fig. 8diagrammatioally illustrates-the opera- .tioncof the pressshownimFig'fl.

.I Fijg. is :an :end ".view of the press shown in Figsfl.

:Fig. .10 is-an ealternative arrangement of the metal ;plate whilerbeingurradiatediromzthe front. :56 paperfeedingmechanism:of Figf'I.

Figs. 11 and 12 illustrate the hot or inking revolution and the cold or printing revolution respectively of the printing procedure using the press shown in Fig. 7.

In the first five figures the use of the invention in one-color printing, such as black and white printing, is illustrated for clarity although the invention is primarily intended for multicolor printing. Any of the embodiments shown are directly applicable to four-color printing, merely by using four similar sets of apparatus respectively with the four color inks, the usual provision for registration of the four colors being made. For example, merely using the arrangement schematically shown in Fig. l, I have produced four-color prints merely by changing the color of by pressure rollers 55 to a paper sheet 56. The

the ink and registering the successive ink trans-,

fers, by hand although the automatic registering embodiments are preferable for obvious reasons.

In Fig. 1 a halftone positive made up of a halftone record H] on a support II is carried on a moving belt i2 and is thereby moved under an ink roller l3 which applies fusible powdered ink M to the surface of the record Ill. The ink powder is supplied from a hopper |5. After a uniform layer of ink M has been applied to the record l0, they are passed together between pressure rollers and on to a hot plate 2|. The hot plate is maintained very accurately at a constant temperature just below the melting point of the ink M by means of a water circulating system including brass tubes 22 soldered to the bottom of the hot plate 2| and through which water from a constant temperature bath 23 is fed by a pump 24.

The record is driven along the hot plate at a constant speed by means of edge rollers 25 which engage the edge of the record. The uniformly heated record then passes on to a moving belt and under a highly intense infrared lamp 3| which is provided with a gold plated reflector 32 which in turn is cooled by water circulating through pipes 33 in the reflector. At this point, the ink adjacent to the black areas |6 of the record I0 is melted as shown by broken lines I? in Fig. 3. The ink particles |8 adjacent to the clear areas I9 of the halftone record are not melted and remain as a powder which can be brushed or blown away after the melted ink has been transferred to a paper support. The arrows 34 in Fig. 3 merely represent the radiation from the lamp 3| and it will be noted that a portion of this radiation passes through the clear areas |9, whereas the rest of the radiation is absorbed into and heats the areas l6.

Referring again to Fig. 1, the record with the melted ink areas is passed, together with paper 35, between pressure rollers 36 at which point the melted ink areas transfer to the paper forming the final image thereon. Any unmelted ink which happens to transfer to the paper is removed by an air squeegee 40. The record together with the rest of the unfused ink particles is moved onto a catch board 4| which is sloped upward and is provided with a rubber cushion 42, in order to catch the rapidly moving record and stop it without damage thereto. The ink is removed from the record and the whole operation repeated.

Fig. 2 differs from Fig. l merely by having transparent support for the record at the point in the printing cycle whereat the record is irradiated with infrared light from a lamp 46. Additional driving rollers 41 are provided for moving the record across the plate 45. Exposure through the record H) as thus provided does not unmelted areas of the ink in some cases still tend to remain as a sheet and may be removed as illustrated at 60 from a record 6|, but in general it is also desirable to apply an air brush or squeegee both to the paper 56 as shown at 62 and to the record 6| as shown at 63.

One of the most satisfactory methods of applying a fusible powder ink to a layer uniformly is by dusting the powder on to the layer. A highly automatic arrangement for doing this is illustrated in Fig. 5. In this figure two positive records I0 and 7| which are to be printed are fastened by clamps 12 onto a large drum 13 which is rotated as indicated by arrow 14 by means not shown. The record 10 is in the stage of being dusted between the points and 8| with a fusible ink which gradually builds up from the point 8|] to the point 8| forming a uniform layer of ink on the record "I. The uniform dusting is provided first by moving a hopper 82 of particles 83 of ink back and forth as indicated by the arrow 84 over an oscillating screen 90. The reciprocating motion of the hopper 82 is provided by a reciprocating drive consisting of a motor 85 driving a drum 86 with oppositely disposed helical grooves 81 engaging a pin 88 on a sliding shaft 89. 7

The powdered ink 83 from the hopper 82 is thus spread evenly in a layer 9| on the screen 90.

This screen 90 is agitated, i. e. oscillated rapidly, as indicated by arrow 92 by means of a cam 93 engaging one edge of the screen and operating against the force of a spring 94. The cloud 95 of ink particles settles uniformly onto the record 16 and as the drum 13 rotates the ink is pressed into firm contact with the record 10 by a pressure roller I00 which is very smooth and cold so that the ink particles have no tendency to adhere thereto. The record and the ink are brought to a uniform temperature just below the melting point of the ink by means of a hot plate |0| disposed inside the rotating drum 13. The inked record is then exposed by infrared radiation from an infrared lamp I02 which is of sufficient intensity to melt the ink adjacent to the dark areas of the positive record 10 but not to melt the ink adjacent to the light areas as the record moves by. The melted ink is then transferred to a paper sheet |03 by means of a pressure roller I04. Any unmelted ink which adheres to the paper I03 is removed by air squeegee I05. The unmelted ink which adheres to the records 70 and 1| is removed by air squeegees I05 and 07 and by a mechanical brush H38. This excess ink N19 is caught in a pan ID and usually I prefer to return the ink to the grinding mill before using it again in the hopper 82.

My copending application referred to repeatedly above describes many ink vehicles suitable for fusion photothermography. They are equally applicable to the present process.

With the present process and using only simple apparatus such as that illustrated in Fig. 1, or at least using four sets of such devices so as the invention involves the application of the colorant in melted form to the record and solidification thereof in situ.

By way of specific example, in one procedure I make up a magenta ink powder consisting of 70 parts of a fusible vehicle, phenyl salicylate or triphenyl phosphate or preferably, benzophenone. To this I add parts of a'colorant (rhodamine 33 extra in the case of magenta), 5 parts of dry soap for anti-static purposes and 20 parts of fine white silica as a separator. This is all reduced to a fine dust in a suitable mill. For each impression the discrete ink is distributed upon the selective absorber, namely the halftone positive image, and exposed from either or both sides to a light source rich in infrared. Only suflicient exposure is used to melt the fusible material adjacent to the black areas of the'positive. Phenyl salicylate remains fluid for some time even upon a cool surface whereas benzophenone solidifies much more rapidly. In either case, before the vehicle solidifies, the fused image is transferred to the print stock which may be either paper or a film pellicle. It has been found that the spatial selectivity which corresponds to the resolving power, is inversely proportional to the exposure time and to some extent to the thermal conductivity of the material of construction. According to a second procedure, the soap is omitted and the fusible compound is melted with the colorant, which, in the case of an insoluble pigment, is dispersed minutely by a supersonic oscillator inserted in the liquid. This is fed quantitatively to the surface of the selectively absorbing layer, which is fastened to the surface of a rotating cylinder. The warm ink is applied dropwise from a line of controllable valves in an ink reservoir. The ink dro-ps are quickly spread out by an air or vapor squeegee or by an electrostatic field. The temperature of the cylinder is maintained below the solidification point of the ink, which is crystallized quickly and in uniform, fine, crystals by supersonic vibrations applied to the ink or the support. The inked surface then passes under a line radiator then into contact with the paper stock, then under a hot suction squeegee to remove the unused ink, and then under the ink applicator again.

Another method of removing unused ink and applying fresh ink that uses a single device is to have an inking cylinder kept above the melting point of the ink, with a porous metal surface, tightly connected with an ink well in the cylinder that has hydraulic or pneumatic connections leading to a pump or plunger. With suction on the reservoir, the warm, porous metal melts all the unused ink, which is drawn into the porous metal, pressure is then applied to force ink out through the porous member and onto the surface of the absorbing layer, whereupon the other operations described above take place.

By way of example of the effect of exposure time on resolving power, it is noted that with pure triphenyl phosphate a resolution of 50 lines per inch is obtained with a one second exposure whereas a resolution of 300 lines per inch requires an exposure of about /100 of a second. However, these limits will probably change with varying conditions and are to be interpreted only relative to one another, not as absolute.

As mentioned above, the thermal conductivity of the record support has some effect but not as great as originally expected. The support may be of glass which has considerably higher conductivity than film or it may be of metal if there is a good heat insulator between the metal and the fusible ink. For example, when a gelatin silver positive on glass .055 thick is maintained at a temperature just below the melting point of the fusible vehicle, the required fusion takes place with exposure not appreciably higher than with such positives on thin films over an air space. On the other hand, I prefer to include an insulating layer of a synthetic plastic such as polystyrene between the record and any highly thermal conducting support. It is also an advantage to use as thin a layer of gelatin as possible for the image layer because of the thermal conductivity of gelatin.

The thermal diffusivity coefficients are 0.0057 for glass, 0.001 for gelatin or cellulose acetate and as low as 0.0006 for certain polystyrene resins. Silver absorbs heat 300 times as fast as glass and proportionately faster relative to the other materials just mentioned. For the source of radiation, standard drying lamps in 250, 500 or 1000 watt sizes are highly efiicient when used with gold plated reflectors and have a life greater than 5000 hours. They are quite satisfactory with just a simple reflector as illustrated up to line per inch quality and are therefore useful for poster and medium quality commercial work. The 1000 watt lamp requires about .05 second minimum exposure to supply the calories required for fusion unless some condenser system in addition to the gold plated reflector is used giving a narrow line of concentrated radiation for scanning the printing surface with only .01 second or even less local exposure. These shorter exposures permit higher quality work as pointed out above.

The two tone positives may have various forms as described above. Films giving 4.0 maximum density have proven to be quite satisfactory but even with the maximum density as low as 1.5, only 10% more photothermal exposure is required and the differential between clear areas and dot areas is still sufiicient. When using the fused ink layer as in Fig. 7 instead of the powdered layers of Figs. 1 and 5 and to some extent even with the powdered layers, the pin point dots of the highlights tend to require greater exposure time than shadow dots. This is solved by the usual expedient of photoengraving, namely the use of large dots in the highlights. The photothermal process according to the examples just described, tends to give clean whites with high contrast in the highlights.

The following table gives a number of suitable ink vehicles mainly by way of illustrating the large choice of materials which 15 available:

1 Ideal; of Q usion, Name M. P., C. Gals per Phenyl Sallcylate. 42-43 20.1 Benzoic Anhydride. 42-43 16.5 Benzyl Phthalate. 42-44 16.7 a-Naplithyl acetate. 44-45 Benzyl Succinate. 44-46 16.0 Benzophen one... 47-48 25. 8 Hydrocinnamic a 47-49 Succinonitrile 47-49 11. 5 Triphenyl Phosphate 49-50 20. 3 Ethyl-n-phenyl Carbonate. 16.6 Methyl-o-benzoyl benzoate p-nitro-anisole 1,3, dimethyl 1, 3, diphenyl cyclobutan 51-53 14. 7 Methyl-fl-naphthyl ketonc 53-55 Trichloracetic Acid 54-57 11. 5 Acetophenone Oxime 56-58 13. 2 Dlphenyl 65-67 28. 8

Of the above, benzophenone appears to give the best quality, highest speed, fusion thermographic prints. It is applicable either to black and white printing or multicolor printing, particularly because of its fast solidification. Various properties of the vehiclemust be taken into consideration and some of the above would be objectionable because of their heavy and unpleasant odor or their inability to disperse certain pigments. However, benzophenone appears to be quite satisfactory in all respects and therefore appears to be the No. 1 choice of the materials listed.

As pointed out in the co-filed parent application, the coloring materials used may be either pigment or dyes and are selected according to the color desired.

It is to be understood that the above embodiments are merely illustrative of the preferred forms of the invention and that the invention is not limited to these embodiments.

I claim:

1. The method of printing which comprises (1) forming a positive two tone image record of a material which absorbs infrared radiation and converts it to heat, on a support of low infrared absorption, (2) putting onto the record a uniform layer of ink which contains a coloring material and a vehicle which melts at a temperature between 20 C. and 200 C. and which ink both in its solid state below the melting point and its liquid state immediately above the melting point is stable and does not adversely affect the record and which ink is transferable in its liquid state, (3) bringing the record and the ink layer to a uniform temperature below and within 20 centigrade degrees of the melting point of the vehicle, (4) uniformly illuminating th record with infrared radiation of sufiicient intensity and time to raise the temperature of the ink overlying the infrared absorbing areas of the record above the melting point without melting the ink overlying the other areas of the record (5) pressing a print support layer, which does not react adversely with the ink and which will receive the ink in its liquid state, onto the front of the ink layer with the print support layer at a temperature below the melting point of the ink to fuse the melted areas of the ink layer to the print support layer and (6) separating the print support layer with the ink image fused thereto from the ink layer.

2. The method according to claim 1 in which the putting on of the ink layer uses one whose vehicle has a latent heat of fusion less than 30 calories per cc. and a melting point between" 30 C. and C.

3. The method according to claim 1 in which the ink layer is put on as a compacted powder of particles of said vehicle containing a uniform percentage of coloring material.

ALEXANDER MURRAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,590,648 Sadtler June 29, 1926 2,254,483 Hess et al. Sept. 2, 1941 2,317,789 Marriott Apr. 27, 1943 

